JP2000180535A - Obstacle detecting device for railroad - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect presence of an obstacle at such specific place of a railroad as a level crossing, etc. regardless of its state, moving or standstill, with ease and sure, for contribution to safe operation of railroad vehicles. SOLUTION: A main body unit 1 and a transponder 2 provided facing each other so as to sandwich a pre-set detection range for a specific place are provided, direct diffusion modulation is performed with a transmission carrier wave signal fc using a modulation code M1 at the main body unit 1, the modulated signal is transmitted to the detection range as a radio wave TW, a radio wave RW reflected on an obstacle present in the detection range and the transponder 2 is received, the reception signal is decoded with the transmission carrier wave signal fc, whether a discrimination information from the transponder 2 is contained in the decoded signal IF and whether a Doppler frequency component is contained are detected, and detection of obstacle is directed outside based on detection result ID and DS.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting an obstacle using radio waves, and more particularly to an obstacle (for example, stopping at a railroad crossing) that hinders the operation of a railway vehicle at a specific location on a railway. The present invention relates to an obstacle detecting device for a railway adapted to easily and surely detect a moving bicycle or a car moving in a railroad crossing.

[0002]

2. Description of the Related Art Conventionally, as an example of a technique for detecting a distance or a relative speed to a moving object such as an automobile using radio waves, for example, a method using spread spectrum radio waves (spread spectrum method) is known. . In this method, a detection device is disposed near a place where a vehicle or the like travels to detect the position and speed of the vehicle. Specifically, a radio wave that is spread spectrum from a transmission antenna is transmitted toward a predetermined detection range, and a radio wave reflected on a moving object existing within the detection range is received by a reception antenna, and a signal of the reception radio wave is received. Is demodulated, a correlation is obtained with a coded random signal for spectrum despreading, and the presence of the moving object is detected by extracting a Doppler frequency component.

According to the detection technique using this spread spectrum method, even when external noise or interference due to radio waves of the same band frequency is received, the spread spectrum / despread processing makes it difficult to be affected by this. Even if there are reflected radio waves from various directions and distances such as the ground and buildings other than the object to be detected, automobiles out of the detection range, for example, it is possible to remove unnecessary signals in the vicinity by setting a distance gate, for example. Further, since the detection range can be set, there is an advantage that measurement in a relatively short distance range is easy.

[0004]

The detection technique using the conventional spread spectrum method has the advantages described above, but when the object to be detected is stationary (stopped), it is reflected from the object. Since the modulated radio wave is not modulated by the Doppler effect, the Doppler frequency component cannot be detected. Therefore, the presence of a stationary (stopped) object can be reliably detected unless some other means is used. There was a problem that it could not be done.

The present invention has been made in view of the above-mentioned problems in the prior art, and makes it possible to easily and reliably detect the presence of an obstacle at a specific place such as a railroad crossing regardless of whether the obstacle is moving or stationary. It is another object of the present invention to provide a railway obstacle detection device that can contribute to the safe operation of railway vehicles.

[0006]

According to the present invention, there is provided an apparatus for detecting an obstacle that hinders the operation of a railway vehicle at a specific location on a railway, comprising: A main unit disposed near one side of a preset detection range at the specific location, and a transponder disposed near the other side of the detection range so as to face the main unit, The transponder has antenna means for transmitting and receiving a radio signal to and from the main unit, and generates identification information unique to the transponder, and incorporates the identification information into the radio signal received by the antenna means. A circuit for sending back to the antenna means, wherein the main body unit comprises:
An oscillator for generating a carrier signal for transmission, a code generation circuit for generating a coded two-phase random signal for modulation, and using the generated coded two-phase random signal to directly transmit the transmitted carrier signal A modulation circuit that performs spread modulation, and transmits the modulated transmission carrier signal as a radio wave toward the detection range, and transmits the radio wave reflected from an obstacle existing within the detection range with respect to the transmitted radio wave and Antenna means for receiving a radio wave returned from the transponder, a demodulation circuit for demodulating the signal of the received radio wave with the transmission carrier signal, and whether or not an output signal of the demodulation circuit includes identification information from the transponder An identification information detection circuit for detecting whether or not, a Doppler signal detection circuit for detecting whether or not a Doppler frequency component is included in the output signal of the demodulation circuit; A circuit for externally instructing detection of an obstacle existing within the detection range based on each detection signal of the identification information detection circuit and the Doppler signal detection circuit. Is provided.

[0007] According to the configuration of the railway obstacle detection device of the present invention, when the object to be detected is stationary or stopped, the radio wave transmitted from the antenna means of the main unit toward the detection range is used. On the other hand, since the identification information unique to the transponder is incorporated in the radio wave returned from the transponder existing within the detection range, the identification information detection circuit of the main unit detects the presence or absence of the identification information. It is possible to detect whether an obstacle (an object that is stationary or stopped) exists within the detection range.

That is, if the identification information is included in the signal received by the antenna means of the main unit, there is nothing between the transponder and the main unit, and no obstacle exists in the detection range. It is detected that it does not exist. If the received signal does not include the identification information, the radio wave (radio wave with the identification information) emitted from the transponder is obstructed by some kind of obstacle, and the obstacle is within the detection range. The presence of the object is detected.

On the other hand, when the object to be detected is moving, the radio wave transmitted from the antenna means of the main unit toward the detection range is reflected by the radio wave reflected from the moving object existing within the detection range. Is modulated by the Doppler effect, the Doppler signal detection circuit of the main unit detects the Doppler frequency component to detect the presence of an obstacle (moving object) within the detection range. Can be detected.

As described above, according to the present invention, whether or not an obstacle is stationary (stopped) or moves at a specific place such as a railroad crossing, the presence of the obstacle is easily and reliably detected. be able to. This greatly contributes to the safe operation of railway vehicles. The details of other structural features and operations of the present invention will be described using the embodiments described below with reference to the accompanying drawings.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a basic configuration of a railway obstacle detecting device using a spread spectrum system according to an embodiment of the present invention. In the present embodiment, as will be described later, a case will be described in which the present apparatus is arranged near a railroad crossing as a specific place on a railway.

The obstacle detecting device for a railway according to the present embodiment has, as a basic configuration, a main unit 1 which performs a main function for detecting an obstacle present in a railroad crossing, and the main unit 1. And a transponder 2 which performs an auxiliary function for detecting the obstacle by transmitting and receiving radio waves. In the main unit 1, 10 is an oscillator for generating a carrier signal fc for transmission, 11 is a directional coupling circuit for distributing the output fc of the oscillator 10 to a signal for transmission and a signal for demodulation of a received signal, and 12 is a spectrum, respectively. A code generation circuit 13 for generating variable coded two-phase random signals (modulation codes) M1 and M2 for spreading and spectrum despreading is used for transmitting a carrier signal fc supplied via a directional coupling circuit 11. A modulation circuit that performs spread spectrum modulation using a modulation code M1 output from a code generation circuit 12, and a detection range 14 that is set in advance at a level crossing of the signal modulated by the modulation circuit 13 (R in FIG.
1, a range indicated by R2).

Reference numeral 15 denotes a radio wave RW reflected from an obstacle existing within the detection range with respect to the transmitted radio wave TW.
And a receiving antenna 16 for receiving the radio wave RW returned from the transponder 2. A signal 16 of the radio wave RW received by the antenna 15 and a part of the output of the directional coupling circuit 11 (a signal for demodulating a received signal, that is, a local signal) And an amplifier circuit 17 for amplifying the output IF of the demodulation circuit 16.

Reference numeral 18 denotes an output of the amplifying circuit 17 (a signal obtained by amplifying the output IF of the demodulating circuit 16).
An identification information detection circuit for detecting whether or not identification information (described later) is included in the output from the amplifier; 19, a Doppler signal detection circuit for detecting whether or not the output of the amplifier circuit 17 includes a Doppler frequency component (described later) Is shown. The Doppler signal detection circuit 19 includes a correlation circuit 20 and a Doppler filter 21.
have. The correlation circuit 20 correlates the output (amplified signal after demodulation) of the amplification circuit 17 with the coded two-phase random signal (modulation code) M2 for spectrum despreading generated from the code generation circuit 12. It has a function to take. In this case, the modulation code M2 generated from the code generation circuit 12 is the same code as the modulation code M1 obtained by performing spread spectrum modulation on the transmission carrier signal fc, and the radio signal reciprocates within the detection range. Is set to have a sign whose phase is delayed by the time required for. Further, the Doppler filter 21 has a function of extracting only the Doppler frequency component included in the output signal of the correlation circuit 20.

Reference numeral 22 denotes a detection signal of the identification information detection circuit 18 (a signal indicating that the identification information ID is included).
And an obstacle detection circuit for externally instructing detection of an obstacle existing within the detection range on the basis of a detection signal of the Doppler signal detection circuit 19 (a signal indicating that the Doppler frequency component DS is included). . On the other hand, in the transponder 2, 30 is a transmitting / receiving antenna for transmitting / receiving a radio signal between the transmitting antenna 14 and the receiving antenna 15 of the main unit 1, and 31 generates identification information (the above-described ID) unique to the transponder 2. Also, an identification information generation circuit that incorporates the identification information into the radio signal received by the antenna 30 and sends it back to the antenna 30 side, and 32 transmits the radio signal received by the antenna 30 to the identification information generation circuit 31, A circulator for transmitting a signal incorporating identification information output from the antenna 31 to the antenna 30; 33, a rechargeable power supply such as a battery for supplying power to the identification information generating circuit 31; 34, a solar battery; 4 shows a circuit for charging the rechargeable power supply 33 by receiving the electric energy converted at 34.

In this embodiment, the radio signal transmitted and received between the main unit 1 and the transponder 2 is a frequency (30 GHz to 1 mm) in a millimeter wave band (wavelength: 10 mm to 1 mm).
(300 GHz). This is because there is an advantage that a large amount of information can be handled because the frequency band is relatively wide, and an advantage that high-resolution sensing can be performed because of high directivity.

The identification information (ID) unique to the transponder 2 includes information for specifying the position of the transponder in the above-described preset detection range. FIG. 2 schematically shows an example of a specific installation form of the railway obstacle detection device according to the present embodiment. In the figure, (a) is a plan view showing an installation form of the present apparatus at a railroad crossing, and (b) is a view seen from a side.

In the installation example shown in FIG. 2, two main units 1a and 1b (each of the main units 1a and 1b shown in FIG. 1) are provided.
And four transponders 2a to 2d, corresponding to each main unit, respectively.
2e to 2h (each the same as the transponder 2 shown in FIG. 1) are arranged. In addition, 40 is an alarm, 4
Reference numerals 1 and 42 each indicate a circuit breaker.

In FIG. 2A, a portion surrounded by a dotted line indicates a range in which the transmission radio waves from the transmission antennas of the main units 1a and 1b are projected, and a projection range of these transmission radio waves. Part R indicated by hatching inside
Reference numerals 1 and R2 each represent the above-described preset detection range. As shown, each main unit 1a, 1b
Are disposed near one side of each of the detection ranges R1 and R2, and each of the four transponders 2a to 2d and 2e to
2h is disposed near the other side of the detection ranges R1 and R2 so as to face the main units 1a and 1b, respectively.

The detection ranges R1 and R2 are determined in consideration of the width and length of the railroad crossing so that other objects existing outside the railroad crossing (that is, objects not to be detected as obstacles) are erroneously detected. It is necessary to adjust appropriately. Specifically, in each of the main units 1a and 1b, the initial setting of the phase difference between the coded two-phase random signals M1 and M2 supplied from the code generation circuit 12 to the modulation circuit 13 and the correlation circuit 20, respectively, is appropriately performed. , The detection ranges R1 and R2 can be set arbitrarily.

Next, an obstacle detecting operation by the apparatus of the present embodiment will be described with reference to FIGS. FIG.
4 detects a stationary object (in the illustrated example, a car stopped at a railroad crossing), and FIG. 4 illustrates a moving object (in the illustrated example,
(A car moving inside a railroad crossing) is illustrated, and in each figure, (a) is a plan view showing the state of obstacle detection, and (b) is a side view. FIG. FIG. 5 shows signal waveforms of the respective units relating to the operation of detecting a moving object.

When detecting a stationary object (see FIG. 3), first, the transmitting antenna 14 of the main unit 1a is detected.
The radio wave TW in the millimeter wave band, which is spread spectrum from, is transmitted toward a predetermined detection range R1 at a railroad crossing.
Each transponder 2a to 2d existing within the detection range R1
Then, the unique identification information IDa, IDb, IDc, and IDd of each transponder is incorporated into the radio signal (the transmission radio wave TW from the main unit 1a) received by each antenna 30, and the signal is transmitted back to the main unit 1a. I do. However, in this case, the transponders 2a and 2b having no obstacle (that is, a stopped car) between the main unit 1a and the transponders 2a and 2b respectively have the identification information ID.
a, IDb is incorporated in the main unit 1a
However, as for the transponders 2c and 2d in which an obstacle exists between the transponders 2c and 2d, the radio signals incorporating the identification information IDc and IDd, respectively, are reflected by the obstacle as shown in the figure. In the end,
It does not reach the main unit 1a.

In the main unit 1a, the receiving antenna 15
Receive the radio signals (reception radio waves RW) from the transponders 2a and 2b, and each identification information ID included in the reception radio waves.
After demodulating a and IDb by the demodulation circuit 16, the identification information detection circuit 18 specifies the transponders (in this case, 2a and 2b) that transmitted the identification information. That is, it detects which of the transponders 2a to 2d is receiving a radio wave. in this case,
Since the radio waves from the transponders 2c and 2d are not detected, the transponders 2c and 2d and the main unit 1a are not detected.
There will be obstacles in between.

Therefore, the obstacle detection circuit 22 detects the detection range R based on the detection result ID of the identification information detection circuit 18.
Obstacles present within 1 (ie, stopped car)
Can be easily and reliably detected. Also, identification information IDa, ID unique to each of the transponders 2a to 2d.
Since b, IDc, and IDd each include information for specifying an arrangement position of each transponder in the detection range R1, it is necessary to accurately detect the position of the obstacle in the detection range R1. Can be.

On the other hand, when detecting a moving object (see FIGS. 4 and 5), the main unit 1
a predetermined detection range R at a level crossing of the radio wave TW in the millimeter wave band spread spectrum from the transmission antenna 14 of FIG.
Send to 1. FIG. 5A shows an example of the transmission radio wave TW subjected to the spread spectrum. In the figure, fc represents the transmission carrier frequency.

This transmission radio wave TW is reflected by an obstacle (that is, a moving automobile) existing within the detection range R1. The main unit 1a receives the reflected radio wave (received radio wave RW) by the receiving antenna 15. Since the reflected radio wave is modulated by the Doppler effect, it contains a Doppler frequency component DS. An example of the received radio wave RW is shown in FIG. In the figure, f
d represents the Doppler frequency.

After the signal of the received radio wave RW is mixed with the output signal (local signal) of the directional coupling circuit 11 in the demodulation circuit 16, the correlation circuit 20 in the Doppler signal detection circuit 19
, A correlation is obtained with the modulation code M2 for spectrum despreading, and the Doppler filter 21 extracts only the Doppler frequency component DS. An example of the extracted signal is shown in FIG.

Therefore, the obstacle detection circuit 22 easily and reliably detects an obstacle (that is, a moving vehicle) existing within the detection range R1 based on the detection result DS of the Doppler signal detection circuit 19. can do. In the embodiment described above, the configuration example in the case of using the spread spectrum system as the transmission / reception form of the radio wave has been described, but the transmission / reception form of the radio wave is not limited to this. For example, a method (F: using a continuous wave (CW: Continuous Wave) radio wave subjected to frequency modulation (FM)) is used.
(M-CW system) or a system using pulse-modulated radio waves (pulse system). 6 and 7 show examples of the respective systems.

FIGS. 6A and 6B show an embodiment in which the FM-CW system is used. FIG. 6A shows a schematic configuration of the apparatus, and FIG. 6B shows a signal waveform of each section. Elements shown by reference numerals 50, 51, 52, 53, 54, 55, and 56 in the illustrated configuration are different from those of the device configuration of the embodiment using the above-described spread spectrum method (see FIG. 1). , The directional coupling circuit 11, the modulation circuit 13, the transmission antenna 14, the reception antenna 15, the demodulation circuit 16 and the amplification circuit 17, respectively. The functions and actions of each element are basically the same as those in FIG.
This is the same as the embodiment.

In this embodiment, the transmission carrier signal supplied from the oscillator 50 through the directional coupling circuit 51 is frequency-modulated in the modulation circuit 52, and the frequency-modulated signal is transmitted from the transmission antenna 53 to a predetermined frequency. The transmitted radio wave is transmitted as a continuous wave toward the detection range, and the radio wave reflected from the target object existing within the detection range is received by the reception antenna 54 with respect to the transmitted radio wave, and the received radio wave is received by the demodulation circuit 55. The signal of the radio wave and a part of the output of the directional coupling circuit 51 (a signal for demodulating the received signal, that is, a local signal) are mixed, and further amplified by the amplifier circuit 56 to correspond to the difference between the frequencies of the transmitted radio wave and the received radio wave. A beat signal is generated. The frequency of this beat signal is shown in FIG.
Upbeat f _BU or downbeat f
Detected as _BD .

Therefore, by detecting the frequency of the beat signal, it is possible to measure the distance and the relative speed to the target object existing within the detection range. That is, the target object can be detected as an obstacle. In the embodiment using the FM-CW method, malfunctions are liable to occur when radio interference is caused by external noise or the like, and when the detection range is set too small, the frequencies of the transmission radio waves and the reception radio waves are reduced. Has a disadvantage that it becomes difficult to measure the distance to the target object, etc., because the difference becomes small accordingly. However, when the detection range is set relatively large and there is no influence of radio wave interference, Regardless of whether the target object is stationary (stopped) or moving in the detection range, its presence can be reliably detected.

That is, in the embodiment using the above-described spread spectrum system (see FIG. 1), when detecting a stationary (stopped) object, it is necessary to use identification information uniquely assigned to the transponder 2. But this F
This is not necessary in the embodiment using the M-CW method. That is, a transponder becomes unnecessary. FIGS. 7A and 7B show an embodiment in which a pulse method is used. FIG. 7A shows a schematic configuration of the apparatus, and FIG. 7B shows signal waveforms of respective parts.

In the configuration shown, reference numerals 60, 61,
Elements indicated by 62, 63, 64 and 65 are the oscillator 10, the directional coupling circuit 11, the modulation circuit 13, the transmission antenna 14, the reception antenna 15, and the demodulation circuit 16 in comparison with the device configuration of the embodiment of FIG. Respectively.
Also, regarding the function and operation of each element, the modulation circuit 62
Except for this, it is basically the same as the embodiment of FIG.

In the present embodiment, the modulation circuit 62 performs pulse modulation on the transmission carrier signal from the oscillator 60 supplied via the directional coupling circuit 61, and transmits this pulse-modulated signal from the transmission antenna 63 to a predetermined position. The radio wave (transmission pulse) is transmitted toward the detection range, and the radio wave (reception pulse) reflected from the target object existing in the detection range is received by the reception antenna 64 in response to the transmission pulse. Received pulse and directional coupling circuit 6
By mixing a part of the output of No. 1 (a signal for demodulating a received signal, that is, a local signal), and detecting a temporal difference between the transmitted pulse and the received pulse as shown in FIG. It is possible to measure a distance to a target object existing in the interior. That is, the target object can be detected as an obstacle.

In the embodiment using the pulse method, malfunctions are likely to occur when radio interference is caused by external noise or the like, and high speed and wide band signal processing is required when the detection range is set small. However, when the detection range is set relatively large and there is no influence of radio wave interference, the same as in the above-described embodiment using the FM-CW method (see FIG. 6). Regardless of whether the target object is stationary (stopped) or moving in the detection range, its presence can be reliably detected. That is, there is no need to use a transponder as used in the embodiment of FIG.

In each of the above-described embodiments, a case has been described where the detection device is arranged near a railroad crossing as a specific place in a railway. However, it is needless to say that the place where the detector is arranged is not limited to the vicinity of the railroad crossing. For example, it can be arranged near the entrance of a tunnel or near a bridge.

[0037]

As described above, according to the present invention, an obstacle can be easily and irrespective of whether it is stationary (stopped) or moving at a specific place such as a railroad crossing. Detection can be performed reliably, and it is possible to greatly contribute to safe operation of railway vehicles.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a railway obstacle detection device using a spread spectrum system according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a specific installation mode of the apparatus of FIG.

FIG. 3 is a diagram for explaining an example (detection of a stationary object) of an obstacle detection operation by the device of FIG. 1;

FIG. 4 is a diagram for explaining another example (detection of a moving object) of the obstacle detection operation by the device of FIG. 1;

FIG. 5 is a diagram showing signal waveforms of respective units related to the detection operation in FIG. 4;

FIG. 6 is a diagram illustrating a schematic configuration of a device and a signal waveform of each unit when an FM-CW method according to another embodiment of the present invention is used.

FIG. 7 is a diagram illustrating a schematic configuration of a device and a signal waveform of each unit when a pulse method according to another embodiment of the present invention is used.

[Explanation of symbols]

1 (1a, 1b) ... Main unit 2 (2a to 2d, 2e to 2h) ... Transponder 10 ... Oscillator 12 ... Code generation circuit 13 ... Modulation circuit 14 ... Transmission antenna 15 ... Receiving antenna 16 ... Demodulation circuit 18 ... Identification information detection Circuit 19 ... Doppler signal detection circuit 20 ... Correlation circuit 21 ... Doppler filter 22 ... Obstacle detection circuit 30 ... Transmission / reception antenna 31 ... Identification information generation circuit DS ... Doppler frequency component fc ... Transmission carrier signal ID (IDa, IDb, IDc, IDd) ... Identification information IF ... Output of demodulation circuit (intermediate frequency signal) M1 ... Encoded two-phase random signal (modulation code) M2 ... The same code as the modulation code and the radio signal reciprocates within the detection range. R1, R2... A preset detection range RW... Received radio wave T ... transmission radio wave

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) G01S 13/91 G01V 3/12 A G01V 3/12 G01S 13/91 Z (72) Inventor Atsushi Sasaki Tokyo 2-2-2 Yoyogi, Shibuya-ku East Japan Railway Company (72) Inventor Keiki Hidaka 345 Kamimachiya, Kamakura-shi, Kanagawa Prefecture Mitsubishi Precision Corporation F-term (reference) 2G005 DA04 5H161 AA01 MM05 MM14 NN11 5J070 AB01 AB17 AB24 AC02 AC06 AD01 AD02 AD05 AE01 AF01 AH04 AH25 AH35 AK22 BC06 BC08 BC20

Claims (6)

[Claims] 1. An apparatus for detecting an obstacle that hinders the operation of a railway vehicle at a specific place in a railway, comprising: a main body arranged near one side of a preset detection range at the specific place. A unit, and a transponder disposed near the other side of the detection range so as to face the main unit, wherein the transponder transmits and receives a radio signal to and from the main unit; and A circuit that generates identification information unique to the transponder, and incorporates the identification information into a radio signal received by the antenna means and sends it back to the antenna means.The main unit transmits a transmission carrier signal. An oscillator that generates the code; a code generation circuit that generates an encoded two-phase random signal for modulation; and the generated encoded two-phase run. A modulation circuit that performs direct spread modulation on the transmission carrier signal using a dam signal, and transmits the modulated transmission carrier signal as a radio wave toward the detection range, and the detection range for the transmitted radio wave. Antenna means for receiving a radio wave reflected from an obstacle present therein and a radio wave returned from the transponder; a demodulation circuit for demodulating the received radio wave signal with the transmission carrier signal; and an output of the demodulation circuit. An identification information detection circuit that detects whether or not the signal includes identification information from the transponder; and a Doppler signal detection circuit that detects whether a Doppler frequency component is included in an output signal of the demodulation circuit. Externally instructing detection of an obstacle present in the detection range based on each detection signal of the identification information detection circuit and the Doppler signal detection circuit Railway obstacle detection apparatus characterized by comprising a that circuit. 2. The Doppler signal detection circuit detects a code having the same code as the code of the two-phase random signal for modulation and having a phase delayed by a time required for the radio signal to reciprocate within the detection range. 2. The apparatus according to claim 1, further comprising: a correlation circuit that calculates a correlation between a signal of the correlation signal and an output signal of the demodulation circuit; and a filter that extracts only a Doppler frequency component included in an output signal of the correlation circuit. The obstacle detecting device for railway according to the above. 3. The detection range is set by appropriately setting an initial phase difference between two-phase random signals supplied from the code generation circuit to the modulation circuit and the correlation circuit, respectively. Item 3. The railway obstacle detection device according to Item 2. 4. The railway obstacle detection according to claim 1, wherein a radio signal transmitted and received between the main unit and the transponder has a frequency in a millimeter wave band. apparatus. 5. The railway obstacle detection device according to claim 4, wherein the identification information unique to the transponder includes information for specifying an arrangement position of the transponder in the detection range. 6. The railway obstacle detecting device according to claim 1, wherein a plurality of the transponders are arranged for one main unit.